Week 4 - Oculomotor and Motor Learning

Question 1

what do these visually guided eye movements mean?

• steadying scene against movement
• bring objects of interest to fovea
• change plane of focus

Answer 1

• VOR (vestibuloocular reflex) and OKN (opto-kinetic nystagmus)
• saccades
• vergence and accomodation

Question 2

what does one have when the only thing that is normal is convergence of eyes?

Answer 2

bilateral opthalmoplegia

Question 3

where do visual signals go to generate saccades?

Answer 3

visual signals to eye position signals to decide size of needed saccade
-this info goes into the saccade generator (PPRF in pons), that then transmits it to left and right “plants” to control the eye

Question 4

what decides where and when to look (times the saccade)?

Answer 4

the forebrain via frontal eye field; contralateral control

Question 5

what do the frontal eye fields do?

Answer 5

times the “okay, go!” for eyes to move

-sends signals to pons (horizontal saccade generator) and midbrain (vertical saccade generator)

Question 6

how is convergence done?

Answer 6

CN III nucleus in midbrain to medial rectus

Question 7

what does the superior parietal cortex do?

Answer 7

shows how to run eyes to keep on target

Question 8

what does it mean if someone has abnormal frontal eye fields but preserved pursuit movements?

Answer 8

slower and incomplete saccades (b/c of FEF)
-can follow finger, so the “generators” (horizontal and vertical saccade generators in pons) and “plants” (signals sent to nucleus) are okay

Question 9

what does it mean if someone has oculomotor apraxia but preserved VOR?

Answer 9

can’t do voluntary up/down movements, but the vestibular nuclei are okay, meaning the frontal eye fields are gone
-might need to blink to break fixation on an object, and swing head around exaggeratedly to move eyes

Question 10

what is congenital oculomotor apraxia

Answer 10

can’t do voluntary eye movements like regular apraxia, but this resolves with time

Question 11

how does information get from the PPRF “saccade generator” to lateral and medial rectus muscles? (example if want to turn eyes right)

Answer 11

1. originate in horizontal premotor area in pons
2. excite the right CN 6 nucleus in pons
   - excitatory signal to right lateral rectus and (thru mlf) left CN 3 nucleus to left medial rectus
3. excite the inhibitory bursters in medulla, which inhibit left CN 6 nucleus in pons
   - inhibitory signals to left lateral rectus and (thru mlf) right CN 3 nucleus to right medial rectus

Question 12

what does a left CN 6 palsy look like?

Answer 12

cannot abduct left eye

Question 13

what is internuclear ophthalmoplegia?

Answer 13

adducting eye is slow (most often right)

• caused by lesion in right mlf
• left eye can saccade normally, but right eye is slow and incomplete

Question 14

what happens if there is internuclear opthalmoplegia with a bilateral mlf lesion?

Answer 14

abducting nystagmus b/c can overcompensate

-there is normal convergence b/c that’s from the midbrain (above pons)

Question 15

what are the effects of:

• step change in neural activity
• pulse change
• pulse + step change

Answer 15

1. spike rate causes a spike train that can slowly reach position and stay there, but takes too long
2. burst of activity quickly jerks to position, but slowly drives eye back
3. burst gets to new position, and increasing firing rate keeps it there

Question 16

how are saccades generated?

Answer 16

before entering generator, pause cells decide to look at the target and give inhibitory signal to burst cells

1. in saccade generator, burst cells (target position expressed as “motor error”) give excitatory signals to integrator and CN 6 nucleus
2. integrator gives excitatory signal to tonic cells (holds eye in position after saccade), which gives excitatory signal to CN 6 nucleus
3. CN 6 nucleus sends signal via motorneuron to whatever rectus muscle is necessary

Question 17

what happens if someone has partial burster cell loss? (also known as progressive supernuclear palsy)

Answer 17

slower saccades (b/c no excitatory signal to CN 6) and can’t hold position (b/c no excitatory signal to integrator to tonic cells)

Question 18

what happens if someone has a problem with the integrators or tonic cells in the saccade generators?

Answer 18

can trigger normal saccades (b/c burst cells OK), but can’t hold position (nystagmus)

Question 19

what is opsoclonus?

Answer 19

due to loss of “trigger/pause” cells

-saccade generators can’t get inhibitory input, so will have involuntary saccades